1. Field of the Invention
The present invention relates to a control unit for an electric oil pump.
2. Description of Related Art
A technology is disclosed in Japanese Unexamined Patent Application, First Publication No. 2004-100827 in which there are provided a clutch that is installed between a power source for driving a vehicle and vehicle wheels and that enables driving power to either be supplied or suspended, and an electric oil pump that supplies hydraulic pressure for engaging the clutch. The hydraulic pressure required to engage the clutch is supplied by controlling the revolution speed of the electric oil pump in accordance with the driving condition (i.e., driving load) of the vehicle.
A technology is disclosed in Japanese Unexamined Patent Application, First Publication No. 2003-54279 in which there are provided a clutch that is installed between an electric motor for driving a vehicle and the vehicle wheels and that enables driving power to either be supplied or suspended, an accumulator that accumulates hydraulic pressure for engaging the clutch, and an electric oil pump that supplies hydraulic pressure to this accumulator. Operations of the electric oil pump are controlled so that the pressure in the accumulator reaches a predetermined value or greater.
However, when the revolution speed of the electric oil pump is controlled in accordance with the driving condition of the vehicle as in the technology disclosed in Japanese Unexamined Patent Application, First Publication No. 2004-100827, a considerable time is necessary to raise the hydraulic pressure to the pressure required to engage the clutch. Accordingly, it is difficult for this technology to respond to a rapid acceleration demand from a driver and a slight response delay is generated so that there is a deterioration in drivability.
In contrast, in the technology disclosed in Japanese Unexamined Patent Application, First Publication No. 2003-54279, irrespective of whether the electric motor for driving is operating at low revolutions or at high revolutions (namely, irrespective of the revolution speed of the electric motor), because the hydraulic pressure supplied to the clutch is held at a constant predetermined pressure to match the constant torque that the electric motor is able to output, when the pressure in the accumulator drops below the predetermined pressure, the electric oil pump is driven continuously so as to raise the hydraulic pressure. If this technology is employed, the electric oil pump is operated extremely frequently which tends to cause power consumption to increase.
Therefore, the present invention provides a control unit for an electric oil pump that makes it possible to always secure the hydraulic pressure required to engage a clutch and that makes it possible to reduce power consumption by the electric oil pump.